Advances in Chemical Engi neering and Science , 20 1 1, 1, 77-82
doi:10.4236/aces.2011.12013 Published Online April 2011 (http://www.scirp.org/journal/aces)
Amphiphilic Block Copolymer for Adsorption of
Organic Contaminants
Jae-Woo Choi1, Kyung-Youl Baek2, Kie-Yong Cho2, Natalia Valer’yevna Shim1,3, Sang-Hyup Lee1*
1Water Environment Center, Korea Institute of Science and Technology, Seoul, South Korea
2Hybrid Materials Research Center, Korea Institute of Science and Technology, Seoul, South Korea
3University of Science and Technology, Daejeon, South Kor e a
Received December 24, 2010; January 16, 2011; accepted April 2, 2011
Abstract
In this study, new polymeric adsorbents, 2 types of polystyrene-block-poly (N-isopropylacrylamide) (PSN,
structure of hydrophobic core and hydrophilic shell), were developed and applied for removal of organic
pollutants from wastewater. Encapsulation of organic pollutants by the polystyrene-block-poly (N-isopropy-
lacrylamide) (PSN) resulted in increasing hydrophobicity of the polystyrene with abundant hydrophobic
spaces within the amphiphilic block copolymer. The encapsulation mechanism of BTEX by PSN was inves-
tigated and found to be mainly attributable to the Van der Waals interactions between the aromatic ring of
BTEX and the hydrophobic core of PSN. Polystyrene-block-poly (N-isopropylacrylamide) showed good po-
tential as a novel and cost effective adsorbent for application to wastewater treatment, which can be simply
regenerated and reused using an external temperature changing system.
Keywords: BTEX, Encapsulation, External Temperature Changing System, Polymeric Adsorbent, Van der
Waals Force
1. Introduction
Organic contaminants naturally persist in the environ-
ment, biodegrade slowly, cause significant damage to
natural water systems and consequently present prob-
lems to human health. To remove such toxic organic
substances, water treatment methods such as adsorp-
tion, biodegradation, chemical oxidation (using agents
such as ozone, hydrogen peroxide or chlorine dioxide),
incineration and solvent extraction have been studied.
Among these practical methods, adsorption has been
widely used as an effective method for removal of or-
ganic contaminants from wastewater. Various adsor-
bents, including activated carbon, natural materials and
organoclays, have been investigated for removal of
organic contaminants [1-11]. Although activated car-
bon has high capacity of absorbing toxic organic sub-
stances and can be easily modified by chemical treat-
ment to increase its adsorption capacity, it also has
several disadvantages [12,13]. Powdered activated
carbon is hard to separate from an aquatic system when
it becomes exhausted or the effluent reaches the legal
discharge level. Furthermore, the regeneration of ex-
hausted activated carbon by chemical and thermal
procedures is also expensive and leads to loss of the
adsorbent [14-16]. In addition, biodegradation, che-
mical oxidation and incineration treatments become
exceedingly expensive when low effluent concentra-
tions are required, and produce by-products that can
also cause pollution. Solvent extraction is also expen-
sive and may lead to contamination of groundwater.
Therefore, alternative advanced technologies have to
be investigated, and polymer adsorbents offer advan-
tages over traditional carbon adsorbents since they can
be simply regenerated by washing with a chemical so-
lution, such as acid or alkali, under ambient conditions
[17-19].
In this study, new polymeric adsorbents, 2 types of
polystyrene-block-poly (N-isopropylacrylamide) (PSN,
structure of hydrophobic core and hydrophilic shell),
were developed and applied for the removal of organic
pollutants from wastewater. When this novel material is
discharged into water, micelles form as a unit molecule.
Through hydrophobic binding, the core-organic com-

J.-W. CHOI ET AL. 78
plexes are effective in adsorbing a variety of organic
pollutants from water. It was found that the total mole
cular weight of the PSN and the hydrophobic to hydro-
philic ratio influenced the encapsulation and removal of
BTEX from wastewater.
2. Materials and Methods
2.1. Chemicals and Materials
Carboxyl acid group terminated trithiocarbonate as a
chain transfer agent (CTA) and polystyrene-block-poly
(N-isopropylacrylamide) (PSN) as an adsorbent were
synthesized by previously reported literature (Figure 1)
[20]. Chemicals used for BTEX encapsulation experi-
ment were benzene, toluene, ethylbenzene, xylene and
methanol, all of them were reagent grade and purchased
from Sigma-Aldrich.
2.2. Polystyrene-Block-Poly
(N-Isopropylacrylamide) Analysis
Polystyrene-block-poly (N-isopropylacrylamide) was
characterized via size exclusion chromatography (SEC),
comprised of a Shodex GPC LF-804 column, CTS 30
column oven, Youngrin refractive index (RI) detector
and HITACHI L-6000 pump, with dimethylformaide
(DMF) used as the eluent, at a flow rate of 1.0 ml/min, to
analyze for the molecular weight and polydispersity in-
dex (PDI). Thermo gravimetric analysis (TGA) and dif-
ferential scanning calorimetry (DSC) were used to
measure the weight changes as a function of the temper-
ature and the temperatures and heat flows associated
with thermal transitions in the polystyrene-block-poly
N-isopropylacrylamide), respectively. The conditions
used for the TGA and DSC were temperature ranges of
27 - 1000℃ and –70 - 600℃, respectively, with a sensi-
tivity and heating rate of 0.5 - 100 mcal/sec and 0.1 -
200℃/min, respectively.
2.3. Encapsulation Procedure
The encapsulation reaction was carried out in 25 ml
screw-cap vials, with Teflon-backed septa, and stirred on
a rotary shaker. Sample aliquots of 1 ml were withdrawn
from the reactor at regular time intervals using a syringe.
Multiple experiments were carried out for a given set of
conditions. Preliminary experiments indicated that the
adsorption equilibrium of BTEX was reached at around
24 h, with no appreciable decrease in the adsorbate bulk
concentration for time periods of up to 2 days. Con-
trolled experiments, where there were no reactions with
the adsorbents, were also conducted to confirm that the
decreases in the BTEX concentrations were actually
caused by adsorption onto the adsorbents rather than by
adsorption onto the walls of the glass bottles or from
volatilization.
2.4. Encapsulation Analysis
BTEX standards; 20, 10, 5, 1 and 0.1 mg·L-1, were pre-
pared in deionized water (18 MΏ·cm) by diluting a 1000
mg·L-1 BTEX solution prepared in methanol. Replicate
aliquots of 1 ml were placed in 10 ml Teflon-sealed screw-
caps vials for GC analysis. The standard solutions were
also run to check for the effects. Separate standard solu-
tions of benzene, toluene, ethylbenzene and xylene; 20, 10,
5, 1 and 0.1 mg·L-1, were also prepared for GC analyses
by appropriate dilution of 1000 mg·L-1 solutions of each
compound. Glass bottle experiments were carried out by
bringing 10 ml aliquots of the stock solution into contact
with 20 mg·L-1 for each BTEX solution and 0.05 g of each
adsorbent polystyrene-block-poly (N-isopropylacrylamide)
(PSN) in glass bottles sealed with Teflon- sealed
screw-caps. The bottles were then shaken for 24 h on a
temperature controlled shaker at 20℃ to attain equili-
brium. Gas chromatograph (Varian STAR 3400 CX;
Purge & Trap) equipped with a flame ionization detector
(FID) was used for analysis of the equilibrium concentra-
tion.
3. Results and Discussion
3.1. Polystyrene-Block-Poly
(N-Isopropylacrylamide) Characterization
In this study, 2 types of polystyrene-block-poly (N-iso-
HO SS
O
S
C
11
H
23
Styrene
CTA-COOH
AIBN in bulk at 80
o
C
SS
S
C
11
H
23
HO
O
mNIPAM
AIBN in DMF at 80
o
C
ON
HHO
O
m
SS
S
C
11
H
23
ON
H
n
Polystyrene precursorPolystyrene-block-PolyNIPAM
Figure 1. Synthesis of polystyrene-block-poly(N-isopropylacrylamide) (PSN), using the situational reversible addition
fragmentation chain transfer polymerization (RAFT) of styrene and N-isopropylacrylamide, from the carboxyl acid group
terminated trithiocarbonate s and AIBN initiating system.

J.-W. CHOI ET AL. 79
propylacrylamide) (PSN) were synthesized for applica-
tion to the encapsulation of BTEX compounds in
aqueous phase. The molecular weight (Mw), weight per-
cent (Wt) and poly dispersity index (PDI) values of each
PSN are presented in Table 1. The well-defined amphi-
philic block copolymers obtained with relatively narrow
molecular weight distributions (PDI < 1.2). PSN 01 and
PSN 02 had different polystyrene Mw, but the Mw of PSN
with almost the same as the Wt of P-NIPAM (Poly-N-
isopropylacrylamide). The amount of polystyrene is crit-
ical, as styrene is hydrophobic, and allows for enlarged
encapsulation room, which influences the capacity for
BTEX removal. In addition, the Wt of PNIPAM is sig-
nificant because N-isopropylacrylamide makes to solubi-
lized the PSN polymer and introduce the PSN polymer to
LCST (Low Critical Solution Temperature) system.
The TGA and DSC curves for adsorbent, polystyrene-
block-poly (N-isopropylacrylamide) and the pure adsor-
bent resulting from the RAFT (Reversible Addition
Fragmentation chain Transfer) polymerization, are
shown in Figure 2. According to the TGA curve, an ab-
rupt weight decrease about 94.8% was occurred within
397 to 436˚C and the polystyrene-block-poly (N-iso-
propylacrylamide) was almost volatilized about 99.6% at
870℃. In temperature range 67.5 to 108.1˚C, the PSN
had a heat capacity about 138.1 J·g-1, as shown in Figure
2. This means that the PSN is very stable below 67˚C
and can be recovered using an external temperature
changing system (32˚C) after BTEX treatment. This
thermal characteristic of PSN allows to be easily and
safely separated of encapsulated BTEX.
3.2. Encapsulation Studies-Removal Capacity of
BTEX
When PSN is discharged into water, it forms micelles as
unit molecules (Figure 3). In the adsorption mechanism
of aromatic compounds existed in the liquid phase into
the PSN, the main type of interactions are Van der Waals
forces. The hydrophobic core activated the linked ad-
sorptive aromatic ring and localizes its hydrophobic in-
teraction. The encapsulation of BTEX by the polysty-
Table 1. Characterization of polystyrene-block-poly (N-iso-
propylacrylamide).
Mw of
PS PDI of PS Mw of PSN PDI of PSN Wt (%) of PNIPAM
PSN01 4,560 1.14 48,000 1.36 82.9
PSN02 23,900 1.13 31,800 1.42 82.1
*PS: Polystyrene; **PNIPAM: Poly(N-isopropylacrylamide); ***PSN:
Polystyrene-block-poly(N-isopropylacrylamide); ****Mw: Molecular
weight; *****Wt: Weight percent; ******PDI: Polydispersity Index.
(a)
(b)
Figure 2. TGA(a)/DSC(b) curves of polystyrene-block-poly
(N-isopropylacrylamide).
in waterEncapsulationBTEX
External Temperature Changing System
Recovery
in waterEncapsulationBTEX
External Temperature Changing System
Recovery
Figure 3. Efficient BTEX encapsulation and recovery me-
chanism using polystyrene-block-poly (N-isopropylacry-
lamide).
rene-block-poly (N-isopropylacrylamide) was slow dur-
ing the initial 12 h and reached an equilibrium state after
24 h. Figure 4 shows the equilibrium concentration after
BTEX encapsulation treatment using the PSN series. For
PSN 01, BTEX encapsulation was effective in the order
benzene > toluene > ethylbenzene > xylene. This trend
was in agreement with the molecular weights of BTEX
compounds (benzene < toluene < ethylbenzene < xylene).
This suggested that smaller molecules are more easily
encapsulated into the hydrophobic vacancy. The similar
results were shown to another recent research [21,22].

J.-W. CHOI ET AL. 80
benzenetoluene ethylbenzenexylene
Equilibrium Concentration (mgL-1)
0
2
4
6
8
10
PSN 01
PSN 02
benzenetoluene ethylbenzenexylene
Equilibrium Concentration (mgL-1)
0
2
4
6
8
10
PSN 01
PSN 02
Figure 4. The equilibrium concentration after BTEX en-
capsulation treatment by the polystyrene-block-poly (N-
isopropylacrylamide).
All the equilibrium concentrations on the PSN 02 adsor-
bents were lower than those on PSN 01. Consequently, in
this study, PSN 02 was found to be a more effective ad-
sorbent than PSN 01 for equilibrium concentrations of all
BTEX compounds via encapsulation. The amount of
encapsulation, distribution ratio and percent removal, qe
(mg·g-1), KD (mL·g-1) and R (%) in equilibrium concen-
tration, respectively, were calculated as follows:

0ee
qCCVM (1)

0Dee
K
CCCVM (2)

00
%100
e
RCCC 
(3)
where, C0 is the initial concentration of the BTEX solu-
tion (mg·L-1), Ce the equilibrium concentration of BTEX
(mg·L-1), V the volume of BTEX solution (l) and M the
mass of PSN adsorbent (g). In Table 2, the sequence of
distribution ratio is PSN 02 > PSN 01, which is related to
the Mw of PS (23 900 > 4 560). Conversely, the order of
removal capacity for the tested polymers was PSN 02 <
PSN 01, and was dependent on the Mw of PSN (31 800 <
48 000). The result indicates that an amphiphilic block
copolymer with a lower polystyrene molecular weight
and higher PSN molecular weight would have a greater
binding affinity. In other words, the Van der Waals inte-
ractions between the aromatic ring of BTEX compounds
and the hydrophobic core of PSN contribute to the en-
capsulation of BTEX into polymer.
3.3. Encapsulation Studies-Competition in
Mixed BTEX Solution
Solutions containing either a single compound and mixed
compounds were analyzed to verify the difference for
amounts of encapsulation. Different results were ob-
served and it became possible because of competition
between the different organic compounds within the
Table 2. Values of equilibrium encapsulation, qe, distribu-
tion ratio, KD, and percent removal, R (%), by each polys-
tyrene- block-poly (N-i sopropylacrylamide).
AdsorbentsAdsorbates qe (mg·g-1) KD (ml·g-1)R (%)
PSN 01
benzene 3.8791 6,417 97.0
toluene 3.6421 2,035 91.1
ethylbenzene 3.1648 757.9 79.1
xylene 3.0588 649.9 76.5
PSN 02
benzene < 3.9 7,800 80.5
toluene 3.8438 4,920 80.8
ethylbenzene < 3.9 7,800 80.5
xylene < 3.8 3,800 81.0
mixture adsorbed by PSN 01 (Figure 5). Lesser amounts
of BTEX adsorption were observed due to the competi-
tion between the BTEX within mixed solutions. The ad-
sorption of BTEX was; thus, observed to proceed in the
order xylene < ethylbenzene < toluene < benzene. The
tendency for adsorption of organic chemical compounds
(BTEX) is generally explained as being associated with
increasing solubility and decreasing molecular weight
[23,24]. For the observed uptake of BTEX, it appears
that the PSN 01 amphiphilic block copolymer exhibited
different removal capacities (R, %) in the order ben-
zene > toluene > ethylbenzene > xylene (Table 3).
The results of present study showed that polystyrene-
block-poly (N-isopropylacrylamide) is an effective ad-
sorbent for BTEX treatment, with potential application
as a novel and cost effective adsorbent for organic pollu-
tants, which can also be simply regenerated and reused
with LCST characteristics. Taking into consideration not
only the encapsulation of BTEX, but also their decom-
position, further works is in progress to improve the en-
capsulation capacity of the amphiphilic block copolymer
benzenetolueneethylbenzene xylene
Equilibrium concentration (mg L-1)
0
2
4
6
8
10
12
14
B,T,E,X compounds
Total BTE X
benzenetolueneethylbenzene xylene
Equilibrium concentration (mg L-1)
0
2
4
6
8
10
12
14
B,T,E,X compounds
Total BTE X
Figure 5. Equilibrium concentration after BTEX encapsu-
lation treatment by the PSN 01 amphiphilic block copoly-
mer.

J.-W. CHOI ET AL. 81
Table 3. Different equilibrium encapsulation values, qe,
distribution ratio, KD, and percent removal, R(%), into
PSN01 when total BTEX was discharged.
benzene tolueneethylbenzene xylene
qe (mg·g-1) 3.7876 2.8411 2.1251 2.0949
KD (mL·g-1) 3,566 490 227 220
R (%) 94.7 71.0 53.1 52.4
and on the introduction of a photocatalytic amphiphilic
block copolymer.
4. Conclusions
Novel polymeric adsorbents, 2 types of polystyrene-
block-poly (N-isopropylacrylamide) (PSN), were de-
veloped and could be applied for removal of dissolved
organic pollutants from wastewater. When this novel
material is discharged into water, micelles form as a
unit molecule. Encapsulation of organic contaminants
by the polystyrene-block-poly (N-isopropylacrylamide)
(PSN) resulted in increased hydrophobicity of the po-
lystyrene, with abundant hydrophobic spaces within
the amphiphilic adsorbents. This means that the core-
organic complexes are effective in adsorption of vari-
ous organic pollutants by hydrophobic binding. The
encapsulation mechanism of aromatic compounds by
PSN was investigated and found to be mainly attribut-
able to the Van der Waals interactions between the
aromatic ring of BTEX and the hydrophobic core of
PSN is the main kinetics of BTEX removal. Polysty-
rene-block-poly (N-isopropy-lacrylamide) showed good
potential as a new cost effective adsorbent for applica-
tion to wastewater treatment, which can be simply re-
generated and reused by changing temperature of ex-
ternal solution.
5. Acknowledgement
Authors acknowledge that this study was granted by
project No 022-081-044 from the Next-generation Core
Environmental Technology Development Project by the
Ministry of Environment in Korea.
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